The Data Coordinating Center (DCC) for the Dialysis Access Consortium (DAC) will coordinate the scientific and operational aspects of the two on-going DAC randomized placebo controlled clinical trials: the Fistula Trial and the Graft Trial, which will evaluate drug therapies that may reduce the failure and complication rate of arteriovenous grafts and fistulas in hemodialysis patients. The maintenance of adequate and safe access to the circulation is critical to the hemodialysis treatment of patients with ESRD. The specific aim for the Fistula Trial is to determine if the 6-week administration of the anti-platelet drug, clopidogrel, increases the patency rate of newly placed fistulas. A secondary aim is to determine if clopidogrel increases the number of fistulas that are suitable for dialysis. The specific aim for the Graft Trial is to determine if continuous administration of Aggrenox (containing dipyridamole and a small amount of aspirin) prolongs the primary unassisted patency in newly constructed grafts. Systems for data acquisition (via a secure web-based data entry), data management, and quality control are being used. The DCC provides training to clinical center staff, and arranges and actively participates in meetings and conference calls of the Steering Committee. During the recruitment and follow-up phase of each trial, the DCC monitors patient recruitment and compliance and uses the database management system to assure accurate and complete collection of trial data. The DCC also coordinates the supply of study drugs and collection of stored biospecimen samples. An inquiry system is used to resolve data discrepancies. Trial progress is presented in reports to the clinical centers, Steering Committee, and the Data and Safety Monitoring Board. Statistical and interim analyses are performed for each trial with final analyses completed at the end. Trial results will be reported and published. At the end of the study, the data will be archived at the NIDDK Data Repository. If either or both of the study drugs are found to be beneficial, the morbidity, and possibly mortality, of hemodialysis patients will improve substantially. The health care cost of maintaining adequate vascular access should also decrease from its current rate of over one billion dollars per year.